Crystal structure, infrared and 31P nuclear magnetic resonance studies of complexes of tris(2,4,6-trimethoxyphenyl)phosphine with mercury(II) halides

Abstract

The ³¹P NMR spectra of 1:1 solutions of tris(2,4,6-trimethoxyphenyl)phosphine (tmpp) and mercury(II) halides HgX₂(X = Cl, Br or I) in acetonitrile reveal the presence of the ionic complexes [HgX(tmpp)]⁺ and [Hg(tmpp)₂]²⁺. The amount of the first of these two species relative to the second increases from X = Cl to I. The solids which crystallize from tmpp–HgX₂ solutions in acetonitrile contain mixtures of ionic compounds which contain both of these cationic complexes. The first species was identified in the solid state by the observation of ν(HgX) bands in the far-IR spectra. In the X = Cl case, crystals of the complex [Hg(tmpp)₂]²⁺[Hg₂Cl₆]^2– were isolated from the solid product and the structure of this complex was determined by single-crystal X-ray diffraction [monoclinic, C2/c, a= 32.767(5), b= 11.500(2), c= 23.814(4)Å, β= 133.57(1)°, Z= 4 formula units; R= 0.047 for 3461 ‘observed’ reflections]. The cation has C₂ symmetry and the mercury atom environment in this ion is dominated by a close association with the phosphorus atoms of the two attached ligands in a quasi-linear P–Hg–P array, but significant deviations from linearity arise, presumably because of contacts with the methoxy oxygen atoms [Hg–P 2.389(5)Å, P–Hg–P 166.51(9)°]. The Hg ⋯ O contacts involving the nearest ortho-methoxy oxygen atoms on the three phenyl groups in each ligand are 2.726(9), 2.938(7), 3.044(9)Å. The [Hg₂Cl₆]^2– anions have a structure of C_i symmetry in which two mercury atoms with tetrahedral HgCl₄ co-ordination are linked by sharing two bridging Cl atoms. The structural parameters for this anion are similar to those found previously for this species in compounds with other cations. The far-IR spectra of the solids obtained from the other mercury halides reveal the presence of [Hg₂X₆]^2– species in these compounds also. For X = I, the product is predominantly [Hgl(tmpp)]₂[Hg₂I₆].